Shockproof shunt trip unit for tripping open the contacts of a circuit breaker



June. 6, 1967 H. R. SH-AFFER 3,324,423

SHOCKPROOF UNT TRIP UNIT FOR TRIPPING OPEN THE TACTS OF A CIRCUIT BREAKER Filed July 27, 1965 4 Sheets-5heet 1 darzazz/vx, 5755?, $555 T456511,-

June 6, 1967 H. R. SHAFFER 3,324,428

SHOCKPROOF SHUNT TRIP UNIT FOR THIPPING OPEN THE CONTACTS OF A CIRCUIT BREAKER drreaziwq flame, 4 548 j .946!

June 6, 1967 H. R. SHAFFER 3,324,428

SHOCKPROOF SHUNT TRIP UNIT FOR TRIPPING OPEN THE CONTACTS OF A CIRCUIT BREAKER Filed July 27, 1965 4 Sheets-Sheet 3 June 6, 1967 H. R. SHAFFER 3,324,423 I SHOCKPROOF SHUNT TRIP UNIT FOR TRIPPING OPEN THE CONTACTS OF A CIRCUIT BREAKER Filed July 27, 1965 4 Sheets-Sheet 4 United States Patent 3,324,428 SHOCKPROUF SHUNT TRIP UNIT FOR TRIPPTNG OPEN THE CONTACTS (PF A CIRCUIT BREAKER Howard R. Shaffer, Glenside, Pa., assignor to I-T-E Circuit Breaker Company, Phiiadelphia, Pa., :1 corporation of Pennsylvania Filed July 27, 1965, Ser. No. 475,154 7 Claims. (Cl. 335-40) This invention relates to auxiliary tripping units for circuit breakers and more particularly to a shockproof shunt trip unit which may be added to a standard circuit breaker to provide additional operating characteristics thereof.

In a conventional molded case circuit breaker, the occurrence of a fault will be effective to bring about opening of the contacts thereof. It is often desirable, however, to bring about opening of the breaker contacts under other than the existence of overcurrent fault conditions. For example, it may be desirable to automatically trip the breaker from a remote location, or as the result of the occurrence of a predetermined condition, not necessarily an electric overload. Such operation is accomplished by providing an auxiliary tripping means, otherwise known as a shunt trip unit.

Shunt trip units generally comprise an electromagnet and an armature movable in response to energization of the electromagnet to release a normally latched mechanism which trips the circuit breaker operating mechanism and thereby opens the breaker contacts. Such arrangements have given rise to serious problems in that the armature of the shunt trip unit may be moved to its tripping position in response to shock blows impressed upon the circuit breakers in which the device is used. Obviously, the nuisance tripping resulting therefrom is undesirable and furthermore may be injurious to the equipment which the circuit breaker is protecting.

Prior art attempts to eliminate this problem generally involve using counterbalanced or inertial weights to prevent movement of the armature during periods that the breaker may be exposed to shock conditions. Such arrangements may be satisfactory when the shunt trip device is initially installed at the factory by skilled technicians, but continual use and exposure to shock vibration necessitates rebalancin'g and fine adjustment which is either impractical or impossible when the circuit breaker is in field operation and normally maintained by relatively unskilled personnel.

In contradistinction thereto, the instant invention provides a shunt trip device which is insensitive to shock conditions and vibration resulting therefrom and thereby eliminates the necessity of continual adjustment which is inherent in presently available shunt trip devices.

In accordance with the teachings of the instant invention, a shunt trip unit comprises an electromagnet which is energized when it is desired to trip the circuit breaker in response to conditions other than electric overload. An armature is normally biased away from the electromagnet, and by means of a novel locking arrangement, to be described in greater detail, such armature can only be moved to its tripping position in response to energization of the electromagnet. A latch member is rotatable under the influence of a biasing spring from a latching position to a releasing position only when the armature has been drawn into engagement with the magnet. The biasing spring is secured between the armature and latch member and performs a dual function. When the latch member is in its latching position, the spring biases the armature away from the magnet and securely maintains it in an obstructing position within the path of movement of the latch member. Thus, cooperation of the armature, biasing spring, and latch member locks the armature in its position away from the magnet thereby preventing 3,324,428 Patented June 6, 1967 movement in response to shock conditions, while at the same time preventing rotation of the latch member. Additionally, the biasing spring rotates the latch member to its releasing position in response to movement of the armature out of the path of movement of the latch member upon energization of the electromagnet. An operating arm is normally biased to trip the circuit breaker operating mechanism but is maintained in a non-tripping position by the latch member when the armature is obstructing the path of movement of the latch member.

Energization of the magnet rotates the armature into engagement therewith whereby the biasing spring rotates the latch member to its releasing position which allows the operating arm to rotate and thereby trip the circuit breaker operating mechanism. It can be seen that the essence of the instant invention resides in the fact that those parts such as the armature, latch member and operating arm which might normally be sensitive to shock blows to actuate the circuit breaker operating mechanism are locked in place by one part, the armature, which, as described previously, is maintained in a locked position by means of the spring interposed between the armature and latch member.

As a particularly advantageous feature of the instant invention, the shunt trip device is provided with an automatic relatching feature which returns the device to its latched position in response to movement of the circuit breaker contact arm from its closed circuit to its open circuit position.

In the preferred embodiment, opening of the contact arm automatically moves the operating :arm from its tripped position into sliding engagement with the latch member. After a predetermined amount of movement, dependent upon the physical configuration of the latch member and the operating arm a rounded head portion of the operating arm slides past and is retained by the latch member, which during this time has been rotated to its latching position by the operating arm. Simultaneously, the armature is rotated by the biasing spring to its locking position in which it blocks the path of movement of the latch member to complete the relatching operation. It is apparentthat the biasing spring serves another important function in addition to the two described above, in that it rotates the armature into its locking position in response to movement of the latch member toward its latching position during the automatic relatching operation.

Accordingly, it is an object of the instant invention to provide a shunt trip unit which is insensitive to shock conditions.

It is another object of the instant invention to provide a shockproof shunt trip unit for tripping the contacts of a circuit breaker from closed circuit to open circuit positions, such trip unit comprising an electromagnet, an armature normally biased away from the electromagnet to a first position, energization of the electromagnet being effective to move the armature towards the electromagnet to a second position, a latch member normally biased toward a tripping position for operation of the circuit breaker automatic tripping means to trip the contacts thereof from closed circuit to open circuit position, such latch member being maintained away from its tripping position in a latching position by the armature when the armature is in its first position.

Still another object of the instant invention is to provide a shunt trip unit which includes an automatic resetting feature to relatch the shunt trip device in response I to opening of the circuit breaker contacts.

Yet another object of the instant invention is to provide a shunt trip unit, which includes an automatic reresetting feature, and which requires relatively few parts by means of using one part for a plurality of functions.

Other objects and a fuller understanding of the instant invention may be had from the following description in conjunction with the drawings in which:

FIGURE 1 is a perspective view of a molded case circuit breaker which may embody the shunt trip device of the instant invention;

FIGURE 2 is a plan view of the circuit breaker of FIGURE 1 with the cover removed;

FIGURE 3 is a cross-section taken from lines 3-3 of FIGURE 2 looking in the direction of arrow 33;

' FIGURE 4 is a somewhat schematic view of a shunt trip device constructed in accordance with the teaching of the instant invention; and

FIGURE 54 is a view similar to that shown in FIG- URE 4, but shows the shunt trip device in its tripped positions Referring to FIGURES 1, 2 and 3, there is shown a molded case circuit breaker 20, which includes a base 21 and removable cover 22.

Although the instant invention will be described with respect to circuit breaker 20, it is to be understood that such description is merely intended to be illustrative of the application of the instant invention within a cooperating circuit breaker. Obviously, the instant invention may find application within any circuit breaker in which it is desirable to provide auxiliary tripping means in the form of a shunt trip device.

Base 21 is divided into three longitudinal compartments by partitions 23 and 24 with each compartment containing substantial identical current carrying elements and fault sensing elements. In addition, the center compartment contains contact operating mechanism 25 whose operation is effective to simultaneously open contact arm 27 of all three phases. Contact operating mechanism 25 is described in Patent No. 3,155,802 issued Nov. 3, 1964, and assigned to the assignee of the instant invention. Fault sensing means 26 are described in United States Patent No. 3,125,651 issued Mar. 17, 1964, and assigned to the assignee of the instant invention.

The current path passed through each phase of circuit breaker 20 comprises terminal strip 28, bimetal heater 29, strap 30, flexible braid 31, movable contact arm 27, movbale contact 32, stationary contact 33, and terminalstrip 34.

Operating mechanism 25 includes releasable cradle 35 which must be maintained in the latched position of FIGURE 3 in order for contact arm 27 to be in the closed position shown. Cradle 35 is maintained in latched position by having its latch tip 36 engaged by auxiliary latch means 37, which in turn is maintained in position by main latch 38 carried by common tripper bar 39. As is well known to the circuit breaker art, common tripper bar 39 extends across all three phases so as to be operable by the time-delay tripping means, bimetal 41, as well as the instantaneous trip means, armature -42, of all phases. Tripping occurs when tripper bar 39 is rotated sufliciently clockwise from its position of FIGURE 3 to free auxiliary latch means 37 from main latch 38.

As will be more fully explained hereinafter, shunt trip device 45 (see FIGURES 4 and is provided for automatically opening the breaker from a remote location'or as the result of the occurrence of a predetermined condition, not necessarily an electric overload.

Now referring more particularly to FIGURES 4 and 5, these figures illustrate a shunt trip device 45 which comprises an electromagnet consisting of generally U- shaped laminated core 51 having coil 52 mounted to one leg thereof. Lead 53, 54 of coil 52 extend through base 21 and are generally connected across two phases of breaker 20, with a normally open switch (not shown) being connected in series with the coil 52.

An armature 56 is pivoted about pivot pin 58 which includes an arm portion 60 extending transversely with respect to the longitudinal axis of pin 58. The armature is movable from the position shown in FIGURE 4 to thatshown in FIGURE 5 in response to energization of 4 coil 52. When the coil is not energized, spring 62, disposed between the arm portion 60 of pivot pin 58 and a latch member 64, maintains the armature in the path of 62 from the position shown in FIGURE 4 to that shown in FIGURE 5. Rotation of the latch allows operating arm 68 to be rotated by operating spring 70 about pivot point 72, during which time operating arm end portion 74 causes a trip lever 76 to rotate the breaker tripper bar 39, thereby actuating the operating mechanism 25.

FIGURE 5 shows the tripped condition of the shunt trip unit just before the breaker contact arm 27 begins to move from its closed circuit to its open circuit position. It can be seen that the latch member 64 is under the armature 56 and by means of spring 62 will maintain armature 56 in engagement with core 51 even if the core is no longer energized.

In accordance with a feature of the instant invention, when the contact arm 27 is moved toward its open circuit position, the response to actuation of the operating mechanism 25 (see phantom contact arm 27 in FIGURE 4) it moves operating arm 68 from the tripped position shown in FIGURE 5 toward its latch position shown in FIG- URE 4 through relatch spring 80. As the operating arm 68 approaches latch member 64, a curved head portion 68' thereof engages the lower side 64' of latch member 64 and rotates the latch member against the bias of spring 62 from the position shown in FIGURE 5 toward its latched position in FIGURE 4. Simultaneously, while latch member 64 is being rotated in the clockwise direction indicated by arrow 78, spring 62 rotates armature 56 from the position shown in FIGURE 5 back into its locking position shown in FIGURE 4 thereby completing the automatic relatching operation. It will be apparent that the automatic relatching operation described above has been accomplished with a minimum number of parts which result is based in part on the fact that spring 62 and pivot pin 58 have been used to perform multiple functions. Specifically, spring 62 function to rotate latch member 64 from the position shown in FIGURE 4 to that shown in FIGURE 5 whenthe armature 5'6 is rotated into engagement with core 51. Additionally, such spring functions to rotate armature 56 back to its locking position when latch member 64 is being moved by head portion 68 of operating arm 68 during relatching.

Similarly, the pivot 58 performs a dual function in that it serves as the pivot point for armature 56 and furthermore its extending arm portion 60 thereof serves as a lever for rotating the armature 56 in the manner described above.

There has thus been described a shunt trip device which is insensitive to large shock blows, includes an automatic relatching feature and substantially reduces the number of parts by means of a novel arrangement wherein relatively few parts perform a multitude of functions.

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specific disclosure herein, but only by the append ing claims.

What is claimed is:

1. A shockproof shunt trip unit for tripping the contacts of a circuit breaker from closed circuit to open cir cuit position, said trip unit comprising:

an electromagnet;

an armature movable in response to energization of said electromagnet between a first position in which said armature is away from said electromagnet, and a second posiiton in which said armature is drawn into engagement with said electromagnet;

a latch member movable between a latching and tripping position, said latch member being locked in its latching position by said armature to prevent operation of circuit breaker automatic tripping means when said armature is in its first position, said latch member being moved to its tripping position to actuate said circuit breaker automatic tripping means when said armature'is moved toward its second position; and g p a single biasing means secured to both said armature and said latch member lfOl' maintaining said armature in its first position when said electromagnet is in its deenergized state, and for moving said latch member to its tripping position, in responsetomovement of said armature toward its second position.

2. In combination with a circuit breaker having a contact arm and automatic tripping means for moving said contact arm between closed circuit and open circuit positions to interrupt the flow of current therethrough, a shockproof shunt trip unit for actuating said automatic tripping means, said trip unit comprising:

an electromagnet;

an armature movable in response to energization of said electromagnet between a first position in which said armature is away from said electromagnet, and a second position in which said armature is drawn into engagement with said electromagnet;

a latch member movable between a latching and tripping position, said latch member beinglocked in its latching position to prevent operation of said automatic tripping means when said armature is in its first position,- said latch member being moved to its tripping position to actuate said automatic tripping means when said armature is moved toward its second position, and said latch member being returned to its latching position in response to said contact arm moving to its open circuit position upon actuation of said automatic tripping means; and

a biasing means secured to said armature and said latch member for maintaining said armature in its first position when said electromagnet is in its deenergized state, and for moving said latch member to its tripping position, in response to movement of said armature toward its second position, said biasing means further performing the function of returning said armature to its first position after deenergization of said electromagnet when said latch member is returned to its latching position in response to movement of said contact arm to its open circuit position.

3. In combination with a circuit breaker having a contact arm and automatic tripping means for moving said contact arm between closed circuit and open circuit positions to interrupt the flow of current therethrough, a shockproof shunt trip unit for actuating said automatic tripping means, said trip unit comprising:

an electromagnet;

an armature secured to a rotatable pivot pin for rotation therewith in response to energizati-on of said electromagnet, said armature being rotatable between a first position in which said armature is away from said electromagnet, and a second position in which said armature is drawn into engagement with said electromagnet, said pivot pin including an arm portion extending therefrom;

a latch member rotatable between a latching and tripping position in response to movement of said armature, said armature obstructing the path of movement of said latch member to maintain said latch member in its latching position when said armature is in its first position, said armature'being withdrawn from the path of movement of said latch member when said armature is rotated to its second position; and a biasing spring secured to the arm portion of said pivot pin and to said latch member for maintaining said armature in its first position and for rotating said latch member to its tripping position to actuate said automatic tripping means in response to rotation of said armature to its second position. 4. The combination of claim 3, wherein movement of said contact arm from its closed circuit to its open circuit position in response to actuation of said automatic tripping means rotates said latch member back to its latching position whereby said biasing spring returns said armature to its first position. 5. In combination with a circuit breaker having a contact arm and automatic tripping means for moving said contact arm between closed circuit and open circuit positions to interrupt the flow of current therethrough, a shockproof shunt trip unit for actuating said automatic tripping means, said trip unit comprising:

an electromagnet;

an armature normally biased away from said electromagnet to a first position, energization of said electromagnet being efiective to move said armature toward said electromagnet to a second position;

a latch member normally biased toward a first position, said latch member being locked in a second position when said armature is in its first position; and

an operating arm normally biased toward a first position which actuates said automatic tripping means, said operating arm being locked in a second position away from said first position by said latch member when said latch member is in its second position;

movement of said armature to its second position in response to energization of said electromagnet allow ing said latch member to move to its first position, thereby allowing said operating arm to move to its first position to actuate said automatic tripping means.

6. The combination of claim 5, wherein movement of said contact arm from its closed circuit to its open circuit position in response to actuation of said automatic tripping means moves said operating arm toward its second position and into engagement with said latch member to return said latch member to its second postion and thereby lock said operating arm in its second position, return of said latch member to its second position allowing said armature to return to its first position thereby effecting automatic relatching of the shunt trip device.

7. In combination with a circuit breaker having a contact arm movable between closed circuit and open circuit positions, and automatic tripping means for moving said contact arm from its closed circuit to its open circuit position, a shockproof shunt trip unit comprising:

an electromagnet;

an armature secured to a rotatable pivot pin for rotation therewith in response to energization of said electromagnet, said armature being rotatable between a first position in which said armature is away from said electromagnet, and a second position in which said armature is drawn into engagement with said electromagnet, said pivot pin including an arm portion extending transversely away from the longitudinal axis of said pivot pin;

a latch member rotatable between a latching and tripping position in response to movement of said armature, said armature obstructing the path of movement of said latch member to maintain said latch member in its latching position when said armature is in its first position, said armature being withdrawn from the path of movement of said latch member when said armature is rotated to its sec-ond position;

a biasing spring secured to the arm portion of said pivot pin and said latch member for 1 maintaining said armature in its first position and for rotating said latch member to its tripping position in response to rotation of said armaure to its second position; said biasing spring additionally performing the function of rotating said armature to its first position in response to rotation of said latch member to its latching position; and I an operating arm normally biased towards a first position which actuates said automatic tripping means, said operating arm being maintained in a second position away from its first position by said latch member when said latch member is in its latching position, said operating arm being in the path of movement of said contact arm and having a rounded head portion thereof which engagingly slides past said latch member to rotate said latch member to its latching position and lock said operating arm in its second position when said contact arm moves to its open circuit position; movement of said armature to its second position in response to energization of said electromagnet causing said latch member to move to its tripping position to thereby release said operating arm which moves to its first position and actuates said automatic tripping means; actuation of said automatic tripping means effecting movement of said contact arm from its closed circuit to its open circuit References Cited UNITED STATES PATENTS 3/1965 Myers 33520 BERNARD A. GILHEANY, Primary Examiner. R. N. ENVALL, JR., Assistant Examiner. 

1. A SHOCKPROOF SHUNT TRIP UNIT FOR TRIPPING THE CONTACTS OF A CIRCUIT BREAKER FROM CLOSED CIRCUIT TO OPEN CIRCUIT POSITION, SAID TRIP UNIT COMPRISING: AN ELECTROMAGNET; AN ARMATURE MOVABLE IN RESPONSE TO ENERGIZATION OF SAID ELECTROMAGNET BETWEEN A FIRST POSITION IN WHICH SAID ARMATURE IS AWAY FROM SAID ELECTROMAGNET, AND A SECOND POSITION IN WHICH SAID ARMATURE IS DRAWN INTO ENGAGEMENT WITH SAID ELECTROMAGNET; A LATCH MEMBER MOVABLE BETWEEN A LATCHING AND TRIPPING POSITION, SAID LATCH MEMBER BEING LOCKED IN ITS LATCHING POSITION BY SAID ARMATURE TO PREVENT OPERATION OF CIRCUIT BREAKER AUTOMATIC TRIPPING MEANS WHEN SAID ARMATURE IS IN ITS FIRST POSITION, SAID LATCH MEMBER BEING MOVED TO ITS TRIPPING POSITION TO ACTUATE SAID CIRCUIT BREAKER AUTOMATIC TRIPPING MEANS WHEN SAID ARMATURE IS MOVED TOWARD ITS SECOND POSITION; AND A SINGLE BIASING MEANS SECURED TO BOTH SAID ARMATURE AND SAID LATCH MEMBER FOR MAINTAINING SAID ARMATURE IN ITS FIRST POSITION WHEN SAID ELECTROMAGNET IS IN ITS DEENERGIZED STATE, AND FOR MOVING SAID LATCH MEMBER TO ITS TRIPPING POSITION, IN RESPONSE TO MOVEMENT OF SAID ARMATURE TOWARD ITS SECOND POSITION. 